Mobility management is an important attribute in a mobile communication system, and handover is a key part of mobility management, since a reasonable handover act can decrease spending made by the system to realize mobility.
In a LTE system, the state of a User Equipment (UE) can be RRC_CONNECTED and RRC_IDLE. When a UE in RRC_CONNECTED state moves from a serving cell to another cell, it will trigger a cross-cell handover in order to ensure continuity of the services.
During the process of the handover, the UE firstly measures the currently serving cell and the adjacent cell according to a measurement control message issued by the Evolved Node B (eNB) in the LTE system, and processes and analyzes the measurement result according to the handover control parameters in the measurement control message, and if the handover condition is satisfied, then it reports the handover event to the eNB, and the eNB then prepares and executes the handover. In this process, the configuration of the handover control parameter determines whether the time of handover occurrence is suitable or not, if the parameter is configured to be too low and the handover condition can be easily satisfied, then ping-pong handover between the serving cell and the target cell is apt to occur. Ping-pong handover increase the spending of the communication system for ensuring mobility of the user, and thus should be avoided as far as possible.
The current method for avoiding ping-pong handover is: when a UE successfully hands over from a cell 1 to a cell 2, the eNB starts a timer Tpingpong; before the timer Tpingpong times out, if the eNB receives a measurement event report, in which the event type is handover and the target cell is the cell 1, reported by the UE again, then the eNB discards the report, that is, it does not originate handover act to the cell 1. When the timer Tpingpong times out, if the eNB receives a measurement event report with the target cell being the cell 1, reported by the UE again, and the handover condition is satisfied, it is allowed to originate the handover act to the cell 1.
This kind of processing means begins with limiting the handover act of a single UE, which seemingly limits the probability of the occurrence of ping-pong handover, but actually does not reduce the possibility of occurrence of ping-pong handover radically.
In the meantime, the way of using a timer has a problem—there is a high requirement on configuration of the duration of the timer. If the duration is configured to be too short, then ping-pong handover cannot be efficiently controlled; if the duration is configured to be too long, then it may lead to the result that the UE cannot hand over back to the original serving cell in time after the handover if the quality of the target cell is too bad, thus causing a call drop. As shown in FIG. 1, the arrow indicates the moving direction of the user, and after the users hands over from a cell 1 to a cell 2, the second handover back to the cell 1 in a short time period is reasonable, but the method in the prior art limits such a correct handover act, which may cause a call drop due to untimely handover.